The present application claims priority under 35 U.S.C. 119 to Korean Application No. 99-33858 filed on Aug. 17, 1999, which is hereby incorporated by reference in its entirety for all purposes.
1. Field of the Invention
The present invention is related to the manufacture of semiconductor devices, and more particularly, to a method of determining the degree of charge-up induced by plasma according to a plasma process, a method for determining whether a contact hole is open using the same, a method for determining the degree of degradation of a gate insulating layer induced by plasma, and an apparatus therefor.
2. Description of the Related Art
A process of using plasma to etch a material layer is used in manufacturing semiconductor devices. For example, in a process of forming a contact hole which exposes a material layer under an insulating layer by etching the insulating layer, the insulating layer is patterned using plasma as an etching medium. At this time, charge separation may occur in an insulating layer pattern due to the electrical characteristic of the plasma. Ions accumulate inside the contact hole of the insulating layer pattern, that is, on the bottom of the contact hole due to charge separation. This so called charge-up can cause various defects in semiconductor devices. For example, when a contact hole exposing a gate electrode is formed, charge-up caused by the plasma process may degrade a gate insulating layer under the gate electrode.
For example, FIG. 1 schematically shows the distribution of charges which are charged up when a contact hole 45 is formed by a plasma process. The degradation of a gate insulating layer 20 caused by the plasma process is described in detail as follows. During formation of contact hole 45 by a plasma process, charge separation may occur at the bottom and top of the contact hole 45. That is, almost all ions of the plasma which are accelerated by a sheath travel in a straight direction, thus accumulating at the bottom of the contact hole 45 as ions 50. Meanwhile, electrons of the plasma accumulate at the upper portion of the contact hole 45 as electrons 55 due to isotropic angular momentum distribution of electrons. This means that the (xe2x88x92) charges are charged up in the upper portion of the contact hole 45 and the (+) charges are charged up on the bottom portion of the contact hole 45. Such a charge-up phenomenon can occur in a plasma etching process for forming a trench or a line and a space structure, as well as in a process of forming a contact hole such as contact hole 45.
Ions 50 which are accumulated at the bottom of the contact hole 45, the trench or line, or the space structure due to charge separation can have the effect that a positive voltage is applied on the gate electrode 30. This positive voltage can affect the gate insulating layer 20. Charge-up of the gate insulating layer 20 continues while the plasma process continues and charges which are charged up due to charge separation reside after the plasma process is terminated. Accordingly, the effect of applying the positive voltage to the gate insulating layer 20 is maintained. The gate insulating layer may be damaged by charge-up thereof, that is, the effect of continuously applying the positive voltage may degrade gate insulating layer 20. Incidentally, when the plasma process is performed, the charge-up phenomenon caused by the plasma cannot be avoided. Also, it is not possible to prevent the material layer such as the gate insulating layer 20 from being degraded or damaged by the charge-up phenomenon.
Additionally, high integration of semiconductor devices due to a reduction in the design rule results in an increase in the aspect ratio of contact hole 45, for example. Accordingly, the line width of the bottom of the contact hole 45 is reduced and the height of the insulating layer pattern 40 is relatively increased. This makes the degree of charge-up induced by the plasma to the insulating layer pattern 40 severe. Therefore, degradation of the gate insulating layer 20 due to charge-up induced by the plasma becomes severe.
It is thus necessary to measure the degree of charge-up due to a plasma process in order to minimize or prevent damage to or degradation of the gate insulating layer caused by the plasma. A plasma damage monitoring (PDM) method has recently been used for measuring the degree of charge-up induced by the plasma. In the PDM method, the degree of damage to the gate insulating layer caused by the plasma is measured based on a change in capacitance of a wafer including the gate insulating layer. However, since the PDM method has limitations with respect to spatial resolution and calibration, the PDM method is used for measuring the degree of charge-up with respect to a flat material layer. Therefore, the PDM method has limitations in connection with measuring the degree of charge-up with respect to a wafer on which patterns are formed.
The present invention is therefore directed to an apparatus and method for determining charge-up induced by plasma or the degree of charge-up with respect to a wafer on which patterns are formed, which substantially overcomes one or more of the problems due to the limitations and disadvantages of the related art.
It is therefore an object of the present invention to provide an apparatus for determining charge-up induced by plasma or the degree of charge-up with respect to a wafer on which patterns are formed.
It is another object of the present invention to provide a method of determining charge-up induced by plasma or the degree of charge-up with respect to a wafer on which patterns are formed.
It is another object of the present invention to provide a method for determining whether a contact hole is opened.
It is another object of the present invention to provide a method of determining the degree of degradation of a gate insulating layer caused by charge-up induced by a plasma process used to form an insulating layer pattern, the insulating layer pattern having a contact hole which exposes a gate electrode and wherein the gate insulating layer is formed under the gate electrode.
Accordingly, to achieve the first object, there is provided an apparatus for determining the degree of charge-up induced by plasma used for manufacturing a semiconductor device, comprising a wafer on which a plasma process is performed, an electron beam generator for generating a beam of primary electrons for repeatedly scanning a predetermined region of the wafer, a detector installed on the surface of the wafer to be separated from the wafer by a predetermined distance, the detector for collecting secondary electrons generated by the reaction between the primary electron beam and the surface of the wafer and emitted to the outside of the surface of the wafer, and a determination unit for determining the degree of charge-up induced to the surface of the wafer by plasma used for the plasma process from the change in the amount of secondary electrons collected by the detector.
To achieve the second object, in a method for determining the degree of charge-up induced by plasma used for manufacturing a semiconductor device, a wafer, on which a plasma process is performed, is introduced. Secondary electrons generated by a reaction between a primary electron beam and the surface of the wafer that are emitted to the outside of the surface of the wafer are collected by repeatedly scanning the primary electron beam on a predetermined region of the surface of the wafer. The degree of charge-up induced at the surface of the wafer by the plasma used for the plasma process is determined from the change in the amount of collected secondary electrons.
The step of determining the degree of charge-up can be performed as follows. Namely, a sample graph, which shows the change in the amount of collected secondary electrons with respect to the number of scans of primary electrons, is provided. A reference graph, which shows the change in the amount of secondary electrons detected in a standard state where charge-up induced by primary electrons is removed with respect to the number of scans of primary electrons, is provided. The degree of charge-up is determined by comparing the waveform of the sample graph to the waveform of the reference graph.
The number of scans corresponding to the maximum peak point of the sample graph is compared to the number of scans corresponding the maximum peak point of the reference graph and the degree of charge-up is quantized from the degree to which the number of scans of the sample graph is larger than the number of scans of the reference graph in the step of determining the degree of charge-up.
Alternatively, the maximum peak value of the sample graph is compared with the maximum peak value of the reference graph and the degree of charge-up is quantized from the degree to which the maximum peak value of the sample graph is smaller than the maximum peak value of the reference graph, in the step of determining the degree of charge-up.
To achieve the third object, the step of determining whether the contact hole exposes the surface of the conductive layer can be performed as follows. A sample graph, which shows the change in the amount of collected secondary electrons with respect to the number of scans of primary electrons, is provided. A reference graph, which shows the change in the amount of secondary electrons detected in a standard state where the contact hole is opened with respect to the number of scans of primary electrons, is provided. Whether the contact hole is opened is determined by comparing the waveform of the sample graph to the waveform of the reference graph.
In the step of determining whether the contact hole is opened, it is considered that the contact hole is opened when the waveform of the sample graph overlaps the waveform of the reference graph and it is considered that the contact hole is not opened when the waveform of the sample graph is separated from the waveform of the reference graph, or in other words when the sample graph does not overlap on the reference graph. It is determined that the contact hole is not opened when the waveform of the sample graph is separated from the waveform of the reference graph toward an upper direction when the number of scans is no more than 200.
To achieve the fourth object, in a method for determining the degree of degradation of the insulating layer of a semiconductor device after a plasma process, a wafer, which has a gate insulating layer formed under a material layer on which the plasma process is performed, is introduced. A beam of primary electrons are repeatedly scanned on a predetermined region of the material layer and secondary electrons generated by a reaction between the primary electron beams and the surface of the material layer that are emitted to the outside of the material layer are collected. The degree to which the gate insulating layer is degraded by the plasma process is determined from the change in the amount of collected secondary electrons.
The step of determining the degree of degradation of the gate insulating layer can be performed as follows. A sample graph, which shows the change in the amount of collected secondary electrons with respect to the number of scans of primary electrons, is provided. A reference graph, which shows the change in the amount of secondary electrons detected in a standard state where the gate insulating layer is not degraded with respect to the number of scans of primary electrons, is provided. The degree of degradation of the gate insulating layer is determined by comparing the waveform of the reference graph to the waveform of the sample graph.
The number of scans corresponding to the maximum peak point of the sample graph is compared with the number of scans corresponding to the maximum peak point of the reference graph and the degree of degradation of the gate insulating layer is quantized from the degree to which the number of scans of the sample graph is larger than the number of scans of the reference graph, in the step of determining the degree of degradation of the gate insulating layer.
Alternatively, the degree of degradation of the gate insulating layer is quantized from the degree to which the maximum peak value of the sample graph is smaller than the maximum peak value of the reference graph by comparing the maximum peak value of the sample graph to the maximum peak value of the reference graph, in the step of determining the degree of degradation of the gate insulating layer.
The degree of degradation of the gate insulating layer may also be quantized from the degree to which the number of scans of the reference graph is smaller than the number of scans of the reference graph by comparing the number of scans where the peak value of the sample graph is reduced to 0 with the number of scans where the peak value of the reference graph is reduced to 0, in the step of determining the degree of degradation of the gate insulating layer.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.